1. Field of the Invention
The present invention relates to fine powders useful for primary and secondary batteries and to methods for producing such powders, as well as products and devices incorporating the powders. The powders are preferably produced by a spray conversion process.
2. Description of Related Art
Many primary (non-rechargeable and disposable) and secondary (rechargeable) batteries commonly utilize fine powders of an electrode material, such as LiCoO2, LiNiO2 and LiMn2O4. Such powders should have one or more of the following properties: high purity; controlled crystallinity; small average particle size; narrow particle size distribution; spherical particle morphology; controlled surface chemistry; controlled surface area; and little or no agglomeration of particles.
With the advent of portable and hand-held electronic devices and an increasing demand for electric automobiles due to the increased strain on natural resources there is a need for rapid development of high performance, economical power systems. Such power systems require improved means for energy storage.
Electrodes used for such applications should have a high surface area to enhance the energy and power density capabilities of the battery. For these applications, powders of electrode component materials are deposited over a large surface area and are typically impregnated with an electrode light.
To enhance the surface area it is desired that the powder component materials be finally divided and of a relatively narrow particle size distribution. Porous particles are desirable because they provide a large surface area to volume ratio. Similarly, wide distribution of particle sizes have a significant deleterious affect on energy density of the cell. Agglomeration of the particles should also be avoided.
Finely divided powders have been difficult to obtain and to deposit with control over layer thickness and uniformity. For preparation of powders of cathode component materials conventional thermal processing followed by grinding and classification is commonly used. Even after heat treatment and grinding, the conversion may be substantially incomplete and the particle size of the product may be undesirable.
U.S. Pat. No. 5,648,057 by Ueda et al. discloses a method for producing lithium compounds in the form of powders that are useful for battery electrodes. The method includes the steps of reacting metal salts to form a slurry, drying the slurry and heating the resulting residue in an oxidative atmosphere.
U.S. Pat. No. 5,589,300 by Fauteux et al. discloses an aerosol process for producing a precursor capable of being converted into a component of an electrode, such as LiMn2O4.
The foregoing methods generally result in poor control over the composition and microstructure of the powders. The inability to control the fundamental powder characteristics is a major shortcoming for the future development and improvement of secondary and primary batteries.
It would be advantageous to provide a flexible production method capable of producing fine battery powders which would enable control over the powder characteristics as well as the versatility to accommodate compositions which are either difficult or impossible to produce using existing production methods. It would be advantageous to provide control over the particle size, particle size distribution crystallinity, surface area of the powder, pore structure of the powder and compositional uniformity. It would be particularly advantageous if such powders could be produced in large quantities on a substantially continuous basis.